A form of energy damaging to most living tissue, found in a cavern beneath San Francisco and on Devidia II, which leads the Enterprise-D crew to the time-travelling Devidians.
Triolic waves appear in the Next Generation two-part story Time's Arrow. Investigators examining a cavern under San Francisco that contains Data's severed head, five centuries old, find traces of them along with a cellular fossil native to Devidia II.
Very few species use an energy source that produces triolic waves, since long exposure is harmful to humanoids. On Devidia II the same readings lead the away team to beings living slightly out of phase with normal time.
Data is drawn through their portal to 1893. The Devidians are travelling to Earth's past to feed on the neural energy of cholera victims, and the triolic signature is one of the means by which the crew follow and finally stop them.